Explain xkcd: It's 'cause you're dumb.
Cueball has apparently been reading about time travel. He tells Megan about this, and Megan excitedly remarks that she did her college thesis on time travel which basically means that she is supposed to know a lot more about time travel than a guy who has just been "reading" about it.
Cueball, however, continues to ask her if she knows basic facts about time travel (like closed timelike curves, wormholes and exotic matter), like he is investigating if he has discovered facets about it that she would have overlooked while writing a thesis about it. Megan keeps trying to say that since she wrote a Time Travel Thesis, (hence the title of the comic), she already knows all of this and much, much more, and she is obviously getting frustrated by Cueball's attempts to impress her with his "knowledge".
At this point Megan's future-self arrives with a Bzzzzt, having used time travel to arrive at this exact moment in time. It seem she has continued her research and has successfully managed to make a time machine.
The reason she arrives is only to tell her younger self that this conversation with Cueball doesn't go anywhere and isn't important, and so present-Megan can leave and not waste her time anymore. Up till then, Megan was presumably reluctant to break off a conversation on the topic of time travel, since the conversation could potentially have improved, or maybe she was even at first attracted to Cueball and interested because he at least had read about time travel. But once the conversation began to run off track, it came as a relief to know that she could quit without the risk of missing out on anything important. Also, since Megan took the effort to time travel back to this exact moment, that must mean the conversation was so boring and uneventful she kept regretting having this conversation even far into the future to the point where she remembers it as one of the moments that need to be changed with her acquired time travel abilities.
And then she just walks away with her future-self leaving Cueball hanging in the last panel, having invented a completely new way to get out of useless/boring conversations.
Alternatively, future-Megan just makes an excuse to haul present-Megan off in order to prevent the latter from disclosing some details of time travel science to Cueball, which could have unintended consequences. However, using very advanced technology, or even violating physics law, for very mundane ends is very common in xkcd, so using time travel to prevent useless conversation is not surprising from Megan.
In either case, future-Megan finished this conversation before inventing time travel, and thus knows this conversation's outcome. So by coming back, she now changes her own (and Cueball's) future. Of course the general implications of being able to travel like this are enormous, and the paradoxes arising from such a possibility are endless, the most pressing (at the moment) being the grandfather paradox, where a time traveler creates circumstances that negate their existence (such as killing their own grandfather), in this case, Older Meagan going back in time to stop Younger Megan from finishing this conversation, who will eventually become Older Megan but with no reason to go back to tell Younger Megan to stop this boring conversation. It is worth noting, however, that the comic does not inherently cause a paradox: so long as the Megan who didn't finish the conversation stills travels back in time with the knowledge that the conversation needed to be stopped and still saves her younger self from wasting her time, a time loop can be logically sustained. (It is also worth noting that a "Mobius" time loop is also perfectly possible, the grandfather paradox isn't a paradox if quantum entanglement is taken into account - something Megan would no doubt know)
It is possible that Randall may have had some conversations like this, where after having spent a lot of time getting nothing out of it himself, would have wished his future self had come back to tell him to just leave the conversation now.
In the title text present-Megan asks future-Megan about her futuristic googles and what they are for, presumably assuming they are needed for the time travel (maybe it is the backpack?). People from the future wearing weird clothing, often involving eyewear of some sort is a trope in Science-Fiction. Movies like Back to the Future 2 which tried to predict the fashion of 2015 back in 1989 didn't get it right, so this might be a commentary on those movies. However it turns out it's just some old and broken Google Glass. The only reason future Megan wears these is that she attended a party at the club that had a 2010's night theme. The fact that the Google Glass is broken and from 2010 alludes to Randall believing that the project was a fad that and that it will never pan out, even in the future. Indeed that seems to be the case. It seems generally that Randall is no fan of Google Glass, which was also shown earlier in 1251: Anti-Glass and later again in 1304: Glass Trolling. Google Glass has become a recurring theme in xkcd.
This is an indication of how far from the future she has traveled, as Google Glass was first released in the 2010s. It is not clear whether she is wearing Google Glass because it became popular in the 2010s or because it was an esoteric piece of hardware that people would readily associate with the 2010s. Also a 90s party may be thrown today, but not a 2000s party. So it is safe to assume that Megan is at least from the 2030s. Also people attending retro dress-up parties frequently make mistakes and do not dress up exactly in-style, creating some anachronisms, especially if they dress up like they did many years ago.
- [Cueball is facing Megan, talking to her.]
- Cueball: I've been reading about time travel.
- Megan: Cool! I did my thesis on time travel!
- [Cueball is now gesturing toward Megan. An electrical charge of some sort is shown occurring outside the panel in the bottom right corner behind Megan.]
- Cueball: Nice! So you know about closed timelike curves?
- Megan: Yup. Thesis.
- Cueball: Apparently wormholes can use exotic matter to–
- Megan: I know. Like I said–
- Charge: Bzzzt!
- [Megan has turned away from Cueball to the right. Megan from the future, wearing sunglasses, a headset and a machine strapped to her back has entered the frame from the right where the charge appeared.]
- Future-Megan: You can skip this conversation. It doesn't turn out to be important.
- Megan: Oh, thank God.
- [Cueball is standing alone, the two Megans have left the panel.]
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You can skip this comic and discussion page. It doesn't turn out to be important. -- 220.127.116.11 (talk) (please sign your comments with ~~~~)
Any possibility that future Megan actually uses time travel to assist present Megan to exit? Plm-qaz snr (talk) 07:52, 5 August 2016 (UTC)
- Yes for sure --Kynde (talk) 07:51, 5 August 2016 (UTC)
I don't feel like it's mainsplaining and I don't think not have a bad problem that will make it so she will not go to 1812 today. is relevant (maybe an joke, but nothing to do with the comic). 18.104.22.168 08:18, 5 August 2016 (UTC)
- I have deleted that part. Someone deleted mansplaining before I started my edit, and then by the time I was ready there was edit conflicts and it was reentered. I have decided not to do anything about it. He may have a point. --Kynde (talk) 11:51, 5 August 2016 (UTC)
Did someone really decide mansplaining was the right word to use here? Not only is it entirely inappropriate, but it's not exactly a well-known term, so it's liable to confuse people. 22.214.171.124 08:28, 5 August 2016 (UTC)
- Yeah. Cueball's just trying to have a conversation, not trying to act like he knows more than her. If anything, she's being rude by not letting him finish what he was saying. Sure, I know more about computers than my dad, but I let him tell me about his new discoveries. I'm a music major, so I know more about music than a lot of people, but I still let them talk. She not only keeps interrupting him, but goes back in time to avoid the "boring" conversation altogether--and says it all right in front of him. We're not supposed to think she's a decent [person], unlike when Randall stood up for people who happened to have not learned something. Trlkly (talk) 09:17, 5 August 2016 (UTC)
- That's my general problem with the term "mansplaining" anyway. It just assumes malintent where there might be none and is really just an incredibly sexist term.--126.96.36.199 07:13, 8 August 2016 (UTC)
- Well she does try to let him know that he do not have to ask if she knows it, just begin talking about it. It is annoying when people assume that just because they just read something no one else has read about it. And even worse if he doesn't understand that she has used years of he life studying the subject. And if he actually understand but continues that's just bad... --Kynde (talk) 11:51, 5 August 2016 (UTC)
- I don't see why it has to be mansplaining - Cueball just learned about it and thinks its exciting, so he wants to tell others about it. And in most conversations between a noob and an expert, the noob usually needs a point reclarified (especially if the book they just read wasnt written by that expert.) FutureMegan knows this isnt the case though… 188.8.131.52 12:20, 5 August 2016 (UTC)
- Shouldn't we include mansplaining as a possible interpretation though? Mansplaining actually has been added dictionary.com along with the "splain" suffix  Lots of comics have more than one interpretation, so I don't see why this one shouldn't be included especially since it is basically identical to the situation Solnit described in her original essay about the phenomenon.184.108.40.206 21:11, 9 August 2016 (UTC)
I don't think the title text mentions a TimeTravel to 2010. Rather there was a party themed 2010 in the future (Like there are 90's and 80's themed parties nowadays)
--220.127.116.11 10:41, 5 August 2016 (UTC)
- Agree that has been corrected. No one know when the glasses broke but in that future no one probably uses them anymore. --Kynde (talk) 11:51, 5 August 2016 (UTC)
How did future Megan know that the conversation wasn't important if she didn't attend it in her past (in fact, no-one did or would)? A grandfather paradox. At best, she remembered to tell her past self, in which case it's still a bootstrap paradox (and an impressive feat of human memory, though Novikov self-consistency principle might hav helped her "randomly" remember). 18.104.22.168 10:57, 5 August 2016 (UTC)
- Tried to add some more about that paradox and in general. --Kynde (talk) 11:51, 5 August 2016 (UTC)
- I added a little bit explaining what I think is a way for the comic to not be a paradox. While it does seem like the grandfather paradox at first glance, so long as the cause interrupting the conversation is preserved in the effect of the interruption, there's no logical problem (at least, that I've been able to think of). So long as the Megan who didn't have the conversation knows that it doesn't go anywhere and travels back in time to tell her younger self and preserve the loop, it can be easily sustained. Marcus4742 (talk) 19:53, 5 August 2016 (UTC)
- The true question is not whether there is an unsustainable time loop but rather if she has any evidence to say that conversation doesn't go anywhere with certainty, assuming that the time travel follows a closed time-like curve, as cueball talks about, then, (like marcus said) megan stops the conversation then goes back in time to stop the conversation because of the fact she stopped the conversation in the first place, not because she had any knowledge that the conversation was important or not. Alternatively, if the time travel is more of an infinite universe type with branching pathways, then future megan could know the conversation doesn't lead anywhere because she either had it or because closed time-like curves are not in effect. But we're probably over analyzing this. Lackadaisical (talk) 20:56, 5 August 2016 (UTC)
- While she expresses relief at the conversation not going anywhere, what's to say she stops it? Her continuing the conversation regardless of whether it goes anywhere would I think be the simplest way to resolve/avoid this potential paradox. Tahg (talk) 22:27, 11 August 2016 (UTC)
- Well the comic shows that she walks away from the conversation, so we know that the future-Megan achieved her goal to break of a conversation between her younger self (the present-Megan) and Cueball. By assuming that future-Megan has had this conversation, we also either assume 1) that she can either a) change the past (without changing herself in the future, which is a paradox), or b) that she travels between parallel universes. In the latter case she did have the conversation (and keeps having had it) in the universe she came from, and has now just stopped the rest of this conversation happening in a parallel universe, that had run on the same tracks up to this moment in time; or 2) Alternatively traveling in time does not change anything, which would imply that she never finished the conversation, since future-Megan had this experience when she was present Megan. That means this conversation has always happened like shown in the comic, and future-Megan never had anymore of this conversation, because it was always broken by a time traveler. But yes I'm sure this is over-analyzing the comic regarding it's point and pun, but not regarding analyzing the possibility of time travel. A closed loop would still only make a real closed loop if this is the original way the conversation panned out interrupted with time travel, else it would not be closed! --Kynde (talk) 12:13, 15 August 2016 (UTC)
Alright, anyone who is willing to make the claim that "Google Glass will probably become popular in the 2010's" is living in a fantasy world. I've edited it to make the far more accurate claim that it could be either because Glass became popular or because Glass was an esoteric piece of hardware that lived (and died) in the 2010's. 22.214.171.124 15:21, 5 August 2016 (UTC)
Can someone include the explanation what a closed timelike curve is? --126.96.36.199 07:32, 8 August 2016 (UTC)